Substituted dioxanes as herbicides

ABSTRACT

Herbicidal compositions containing compounds of the formula   WHERE R2 is hydrogen, hydrocarbyl or substituted hydrocarbyl radical; R2a is hydrogen or methyl and R2 and R2a may together form a ring; R5 is hydrogen, alkyl, haloalkyl or cyanoalkyl; Rr is aryl, substituted aryl or heterocyclyl.

United States Patent [191 Young et al.

[ 1 Aug, 21, 1973 SUBSTITUTED DIOXANES AS HERBICIDES [75] Inventors:Sanford Tyler Young, Lockport,

N.Y.; Kenneth Lee Hill, Doy1estown,

[73] Assignee: FMC Corporation, New York, NY.

[22] Filed: Feb. 9, 1972 [21] App]. No.: 224,909

Related US. Application Data [63] Continuation-impart of Ser. No.699,204, Jan. 19, 1968, abandoned, and a continuation-in-part of Ser.No. 868,278, Oct. 9, 1969, abandoned, and a continuation-in-part of Ser.No. 182,400, Sept. 21, 1971, abandoned.

[52] US. Cl 71/88, 71/90, 71/94, 260/294.8 D, 260/294.8 F, l60/294.8 G,l60/294.9, 160/297 R, 160/332.3 H, l60/340.7

3,459,771 8/1969 Nikles et a1 260/340.7

FOREIGN PATENTS OR APPLICATIONS 7,013,903 3/1971 Netherlands 71/88 OTHERPUBLlCATlONS Dobinson et al., Aspects of Stereochemistry, etc.", (1961),.1. Chem. 800., pp. 2338-2342.

Baggett et a1., Aspects of Stereochemistry etc.", (1960), J. Chem. 800.,pp. 2574-2581.

Primary Examiner-Lewis Gotts Assistant ExaminerG. Hollrah Attorney-AbnerSheffer et a1.

[57] ABSTRACT Herbicidal compositions containing compounds of theformula where R is hydrogen, hydrocarbyl or substituted hydrocarbylradical; R is hydrogen or methyl and R and R may together form a ring; Ris hydrogen, alkyl, haloalkyl or cyanoalkyl; R is aryl, substituted arylor heterocyclyl.

12 Claims, 14 Drawing Figures PAIENTED MIR 2 I I975 SHEET 05 HF 11 E. K.i

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x 60m wviwu wuwh 3323 33 0355 23 no mcououm m PAIENIEDMIGZI ms 3.753.678

SHEET 11 OF H macaw hus. no mcoponm mconumolm now 930a m :3 m a Go mcopom mg no. 933 wamgass wmkm .5503 33.3 2.3 no u connwo m 93 mo copoum anno. mama pwawc m .3503 30 on no oh .3603 28.5 23 no .m

s n I 0 3 m u 5.3 03 on now xwom po wc m TEWQ 'J 1 Dumas sq; go suoqoadSUBSTITUTED DIOXANES AS HERBICIDES This application is acontinuation-in-part of Ser. No. 699,204 filed Jan. 19, 1968 nowabandoned, Ser. No. 868,278 filed Oct. 9, 1969 now abandoned, and Ser.No. 182,400 filed Sept. 21, 1971 now abandoned.

This invention relates to herbicidal compositions. It has been foundthat there is unexpected herbicidal activity in the compounds of theformula R9 ""z cn." 0411.41

OCfi2 in which there is a cis relationship between the OCl-I R group andany R group other than hydro- R is hydrogen or an alkyl, haloalky,cyanoalkyl, aryl, arylalkyl, aryloxyalkyl, cycloalkyl, arylalkoxyalkyl,alkoxyalkyl, alkenyl (including substituted alkenyl), alkynylalkylthioalkyl, alkylsulfinyalkyl or alkylsulfonylalkyl where any arylradical is phenyl, furyl or thienyl which is unsubstituted or carries asingle X substituent defined below:

R is hydrogen; R is hydrogen, alkyl or haloalkyl such as chloroalkyl orbromoalkyl;

R is a monovalent aromatic phenyl, furyl, thienyl or 2-pyridyl radicalwhich is unsubstituted or has one, two or three, preferably less thanthree, Y" substituents, as defined below:

X", mentioned above, may be H, F, Cl, Br, lower alkyl, trifluoromethyl,lower alkoxy or benzyloxy;

Y, mentioned above, may be H, F, Cl, Br, CN, CF lower alkyl or loweralkoxy.

It is also found that there is herbicidal activity in compounds of theabove formula in which R and R together constitute a single divalentradical having its valences on two different carbon atoms of saidradical so as to form (with the 2-carbon atom of the illustrated dioxanering) a ring. It will be seen that such compounds have a spirostructure, i.e.

with the dotted lines indicating the remaining atoms of said divalentradical. In such spiro compounds, it is believed that the cis and transforms are in resonant equilibrium.

Also, it is found that there is herbicidal activity in compounds of theabove formula in which R is alkyl and preferably less bulky than R (e.g.R may be aryl or isopropyl when R is methyl) and there is acisrelationship between R and the O-CH -R group.

The alkyl radicals are preferably lower alkyl and may, for example, bemethyl, ethyl propyl, isopropyl, n-butyl, isobutyl, sec-butyl or t-butylradicals; thus the alkoxy, preferably lower alkoxy, radicals may, forexample, be methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy,sec-butoxy or tert-butoxy radicals. Any alkenyl or alkynyl radicalspreferably have less than 6 carbon atoms. Preferably each of thesubstituents R R and R has a molecular weight below 125 when it isaliphatic and a molecular weight below 190 when it contains a ring.

Known classical steps may be employed to make thecis-5-arylmethoxy-2-substituted-1,3-dioxane compounds used in thisinvention. They may be made from the correspondingcis-S-hydroxy-l,3-dioxane (e.g. cis- 5-hydroxy-2-phenyl-l,3-dioxane) byetherification with the appropriate compound, e.g. a compound of theformula in xylene or other appropriate solvent. For example, theS-hydroxy-dioxane in solution may be treated with sodium hydride to formthe corresponding sodium alcoholate and the chloride may be addedgradually thereto. The S-hydroxy-dioxane, which is a cyclic acetal, maybe produced by reaction of glycerol and an al dehyde. Such reactionsusually also produce, as byproducts, 4-hydroxymethyl-2-aryll,3-dioxolanes.

The compounds in which R is hydrogen may be made by etherifying, with anarylmethyl chloride (or bromide) the sodium alcoholate of the5-hydroxy-l,3- dioxane resulting from the acetalization of glycerol andformaldehyde. They may also be made by the acetalization reaction offormaldehyde and a Z-arylmethoxy- 1,3-propanediol. The latter may beprepared by known methods, such as by the acid hydrolysis of thecorresponding S-arylmethoxy-Z-aryl-l,3-dioxane; see West and Ludwig, J.Am. Chem. Soc. 74, 4466 (1952).

Alternatively, the dioxanes of this invention may be produced byacetalization reaction of an aldehyde or ketone with the appropriate2-arylmethoxy-l ,3- propanediol. This process is particularlyadvantageous when R is a group e.g. chloromethyl, susceptible to attackby the alkaline reagent nonnally employed in the etherification reactionmentioned above.

Particularly advantageous for preparation of those compounds in which Ris other than hydrogen is the process based upon S-aIkyIidene-l,3-dioxanes. The appropriately substituted 5-alkylidene-l,3-dioxane isepoxidized, the epoxy compound hydrogenated to give the corresponding5-hydroxy5-all yl-l,3-dioxane and that S-hydroxy compound etherified asdescribed above.

Preparation of the 5-cyanoalkyl compounds may be readily accomplished byreaction of the appropriate 5- haloalkyl compound with sodium cyanide.

In the herbidical use of the material, the active cis compound may beused in admixture with the trans isomer, and such mixture may evencontain a major proportion of the latter. Generally it is mosteconomical to use materials of high cis content made by synthesis whichreduce, or avoid, the formation of the trans isomer. The higher the ciscontent the greater is the herbicidal effect of the given mixture ofcis, trans isomers. In the most preferred forms of the invention the ciscompound is present in amount at least equal to that of thecorresponding trans compound, e.g. the cisztrans ration is over 3:2,more preferably over 2:1 and still more preferably at least 3:1. Theaforementioned dioxolanes may also be present in the mixture asimpurities.

When the S-hydroxy-dioxanes used as the starting materials are rich inthe cis forms, the resulting products have a high content of theherbicidally active cis-5- arylmethoxy-2-aryl-1,3-dioxanes. It is alsooften found that on crystallization of the products (as from reactionmixtures containing a solvent such as xylene) followed byrecrystallization (as from benZene-ligroin or benzene-petroleum ethermixtures) the solid products are richer in the active cis compounds, thetrans compounds and dioxolanes being preferentially dissolved.

This invention provides a new class of herbicidal materials, having bothpre-emergent and post-emergent activity. The materials are highlysuitable for the control and elimination of grassy plants, particularlyan nual grasses, in the presence of broad leaved crops, such as cotton,sugar beets, peanuts, soya beans, snap beans, lima beans, tomatoes ornursery stock. Among the compounds found to be especially effective arecis- -(Z-fluorobenzyloxy)-2-phenyl-1,3-dioxane; cis-5-(2-methylbenzyloxy) 2-phenyl-l ,3-dioxane; cis-5-benzyloxy-2-(3-chlorophenyl)-1,3-dioxane; cis-5-benzyloxy-l ,3-dioxane;cis-5-benzyloxy-2-(2-fluorophenyl)-I ,3-dioxane;cis-5-(4-methylbenzyloxy)-2- phenyl-I,3-dioxane;cis-5-(2-bromobenzyloxy)-2-phenyl-l ,3-dioxane;cis-5-(4-fluorobenzyIoxy-2-phenyl- 1,3-dioxane;cis-5-(3-fluorobenzyloxy)-2-phenyl-l ,3- dioxane; cis-5-(2-chloro-benzyloxy)-2-phenyl-I ,3- dioxane;cis-5-benzyloxy-2-(3-fluorophenyl-l ,3- dioxane;cis-5-(2-fluorobenzyloxy)-2-( 3-fluorocis-5-benzyloxy-2-(3-methylcis-5-(2-fluorobenzyloxy)-2-( 3- cis-5benzyloxy-2-( 3- phenyl)-1,3-dioxane; phenyl)-1,3-dioxane; chlorophenyl)-I ,3-dioxane;benzyloxyphenyl)-I,3-dioxane; cis-5-benzyIoxy-2-(3- methoxyphenyl)-l,3-dioxane; cis-5-(2- methylbenzyIoxy)-2-(3-chlorophenyl)-I,3-dioxane;2- c-ethyl-5-r-(Z-fluorobenzyloxy)-5-methyl-1,3-dioxane;2-c-ethyl-5-methyl-5-r-(2-methylbenzyloxy)-1,3- dioxane;5-r-(2-chlorobenzyloxy)- Z-c-ethyI-S-methyl- 1,3-dioxane;2-c-chloromethyl-5-r-(2- fluorobenzyloxy)-5-methyl-l ,3-dioxane;

For compounds having an X or Y substituent other than H, outstandingherbicidal activity, particularly for preemergence application, has beenobserved especially in compounds having that Y substituent at the 2-position (ortho position) of the ring to which it is attached (e.g.,2-chloro-, 2-f1uoro-, 2-bromo, or 2- methylbenzyloxy compounds) and alsoin compounds in which X is at the 3-position (meta-position) of theother ring (e.g., where R is 3-chlorophenyl, 3- methylphenyl,3-fluorophenyl, 3-methoxyphenyl and 3-benzyloxyphenyl). Compounds havingfluoro groups, as in the compounds of Examples 9 and 13, showoutstanding postemergence as well as preemergence activity.

Particularly preferred are those compounds in which R is ethyl orchloromethyl.

The stereochemistry of the derivatives of 5-hydroxy- 1,3-dioxane hasbeen discussed in the scientific literature [see, for example, Baggettet al., J. Chem. Soc., 2574 (1960 and Dobinson and Foster, J. Chem. Soc.2338 (l96l)]. As pointed out in the literature, a cisrelationshipbetween the 5-substituent and the 2- substituent occurs when the5-substituent is in an axial position and the 2-substituent is in anequatorial position. Much information concerning the structures involvedcan be obtained from nuclear magnetic resonance spectra.

The accompanying drawings show nuclear magnetic resonance (nmr) spectraof the following compounds or mixtures:

FIG. I, cis-5-benzyloxy-2-phenyl-l ,3-dioxane;

FIG. 2, trans-5-benzyloxy-2-phenyl-l ,3-dioxane; FIG. 3,4-benzyloxymethyl-Z-phenyl-l,3-dioxolane; FIG. 4, a mixture of thecompounds of FIGS. 1, 2, and 3;

FIG. 5, 5-(2-fluorobenzyloxy)-2-phenyl-l,3-dioxane rich in the cis formthereof;

FIG. 7, cis-5-(2-methylbenzyloxy)-2-phenyl-l ,3- dioxane;

FIG. 7, c-S-benzyloxy-5-methyl-2-phenyl-1,3-

dioxane;

FIG. 8, t-5-benzyloxy-S-methyI-Z-phenyl-1,3- dioxane;

FIG. 9, r-5-ethyl-c-5-(2-fluorobenzyloxy)-5-methyl- 1,3-dioxane;

FIG.I0, r-5-ethyl-t-5-(2-fluorobenzyloxy)-5-methyll,3-dioxane;

FIG.11, c-5-(2-fluorobenzyloxy)-5-rnethyl-r-2-phenyl-l ,3-dioxan;e

FIG.12, t-5-(2-fluorobenzyloxy)-5-methyl-r-2-phenyl-l ,3-dioxane;

FIG.13, c-5-(benzyloxy)-r-2-isopropyl-5-methyl-l ,3- dioxane;

FIG.14, (30%cis).

All spectra were run on a Varian A-60A nmr at 60 mc using CDCI assolvent under normal operating conditions with the sample temperature ca37. In accordance with accepted practice, tetramethylsilane was used asan internal standard in making the measurements.

The cis and transcharacterizations used herein and the estimatedrelative amounts of these species are based on nmr (nuclear magneticresonance) and VPC (vapor phase chromatography) measurements. As seen inFIG. 1 the nmr spectrum of cis-S-benzyloxy-Z-phenyl-l ,3-dioxane shows amultiplet (a jagged peak") at about 3.22 ppm with a base width of about10 cps (indicating the presence of an equatorial proton on the 5-carbon) and also a characteristic peak at about 5.47 ppm. Thecorresponding trans compound (FIG. 2) does not show the same multipletat about 3.22 ppm but shows a characteristic peak at about 5.37 ppm. Themixture of the stereoisomers of the corresponding dioxolane (FIG. 3)shows two peaks at 5.73 and 5.89 ppm. The mixture of all these compounds(FIG. 4) shows the multiplet at 3.22 ppm, but this has a much smalleramplitude than that of the one seen in FIG. 1 owing to the smallerproportion (about one fourth of the mixture) of the cisdioxane compound.FIG. 4 also shows the four peaks between 5.25 and 5.95 ppm previouslydiscussed; the relative proportions of the individual isomers can bedetermined by comparing the individual areas under these peaks, in knownmanner.

In FIG. 5, (for a compound similar to that of FIG. 1, but carrying a2-fluoro substituent on the benzyloxy group), there is a peak at about3.34 ppm. having a base width of about IO cps. There is also acharacteristic peak at 5.54 ppm. In FIG. 6, (for a similar compoundhaving a Z-methyl substituent) there is also a multiplet at 3.32 ppm.having a base width of about 10 cps and a peak at 5.55 ppm.

In FIG. 5, a comparison of the total area under the peaks from about3.84 ppm. to 4.50 ppm. (contributed mainly by the protons at the 4- and6-carbon atoms) with the other information supplied by this nmrspectrum, indicates the presence of S-hydroxy-Z-phenyl- 1,3-dioxane inproportion of about 12 percent.

5-benzyloxy-2-(2-furyl I ,3-dioxane It has been found that the cis andtrans components can be identified by vapor phase chromatography (VPC).In operating with a certain chromatographic column it was found that thedioxolanes were eluted first, followed by thetrans-S-arylmethoxy-2-aryl-l,3- dioxane, and lastly, the correspondingcis-dioxane compound. The column used was a 5 foot column, onefourthinch in diameter, containing percent Carbowax M TPA [terephthalic acidterminated polyethylene oxide] on granules of Chromosorb W(adiatomaceous earth). The instrument used a thermal conductivity detectorwith helium as the carrier gas. The operating temperature of the columnwas 240C and the operating gas flow was 300 cc/min. In the analysis,about 20 microliters of a 10 percent solution of the test sample inbenzene was injected onto the column in well-known manner. The relativeamounts of the individual materials emerging from the column can bereadily determined in conventional manner and these components can beidentified as cis or trans, based on their order of emergence asdescribed above. Incidentally, this order of emergence differs from thatobserved for the corresponding 5-hydroxy-2-phenyl-1,3- dioxane; in thelatter case the cis compound emerges before the trans isomers.

FIGS. 7-l4 show the nmr spectra of the compounds named thereon. Thelegends indicate the significance of the various features of thespectra; the same letter is used for corresponding protons in eachspectrum so that the figures may be correlated. In accordance withconventional practice there are lines for integrations of the variouspeaks and the integrations are done twice, so that there are pairs ofintegration lines. As is conventional, the spectra show an extension ofthe left hand end of the spectrum, displaced upward and to the right sothat the whole spectrum can appear in theavailable space; in the spectrano significant features are apparent in the range represented by thatline. The integrations indicate the areas under the peaks; thus in FIG.7, the area under peak A is equivalent to 3 protons and in FIG. 8, thearea under the broader but lower peak A is also equivalent to 3 protons.

Among the various features evident from a comparison of FIGS. 7 and S,the following differences may be noted. Where there is acis-relationship (FIG. 7), the peak F is at a lower field (i.e. higherppm (8)) and the peak G is also usually at a lower field than is thecase where there is a trans-relationship (FIG. 8); these features arealso evident in FIGS. 1 and 2. Also for the 5- methyl compounds, wherethere is a cis-relationship, peak A is at a higher field and the groupof peaks B, C D, E covers a larger range of ppm than is the case wherethere is a trans-relationship.

The preparation, properties, and herbicidal activity of representativecompounds of this invention are illustrated further in the followingexamples, in which all temperatures are in degrees Centigrade.Additionally, when reference is made to a reduced pressure withoutspecifying that pressure, it is to be assumed that the reduced pressureis that attainable by means of a water aspirator.

EXAMPLE I In this Example there was used a white crystalline sample ofS-benzyloxy-Z-phenyl-l ,3-dioxane of melting point 75-76C. and of highcis content.

The preand postemergence herbicidal activity of this material was testedin the following manner: lima beans, corn, lettuce, mustard andcrabgrass were planted in rows side-by-side in shallow flat-bed traysfilled with a mixture of equal amounts of silt-loam and sandy-loamsoils. The material to be tested was dissolved in an acetone-watermixture and was sprayed on the soil at a rate of 8 pounds per acre forpreemergence screening. In post-emergence screening, plants were sprayedwith the acetone-water solution at a rate of 8 lbs/acre approximatelytwo weeks after planting, i.e. when com plants have developed 3 to 4true leaves. Two weeks after application, the phytotoxicity of thematerial was evaluated for both preand post-emergence tests. Untreatedplants were maintained for comparison in both procedures. There wasessentially complete kill of corn and crabgrass in both preandpost-emergence screenings while none of the other plants were killed.

EXAMPLE 2 In this Example there was used a cis-S-benzyloxy-Z-phenyl-I,3-dioxane sample prepared in the following manner:

To a solution of 16.8 g cis-S-hydroxy-Z-phenyl-l,3- dioxane in 150 mlxylene was added in small portions 4.0 g of a 60 per cent suspension ofsodium hydride in mineral oil. The mixture was then maintained at 40C.for I hour. To this solution was added dropwise 13.9 g benzyl chloride.The reaction mixture was then maintained at 110C. for 6 hours. After thereaction mixture had been cooled, it was filtered and evaporated underreduced pressure. The resulting solid was recrystallized from abenzene-ligroin mixture. The melting point of the recrystallized productwas 7375C. VPC and nmr studies revealed the product to be 80-90 per centcis-5- benzyloxy-Z-phenyl-l,3-dioxane. The product showed excellentselective preand post-emergence herbicidal activity, as shown in thefollowing tabulations in which the numbers represent per cent kill atthe indicated dosages.

Pre-emergence Evaluation at the dosage (in pounds per acre) indicatedbelow Test Plant Species 0.75 1.5 3.0 6.0 Peanuts 0 0 0 0 Rice I00 I00I00 I00 Alsike Clover 0 0 0 Cotton 0 0 0 0 Tomato 0 0 O 0 Wheat 10 I0 9080 Corn 80 80 I00 I00 Meadow fescue I00 I00 I00 100 Sugar beet 0 0 0 ODallisgrass I00 I00 I 00 I 00 crabgrass I00 I00 I 00 I 00 Cucumber 0 0 010 German hay millet I00 I00 I00 I00 Flax 9O 95 Lambsquarter 0 O 0 0Wild oats 75 60 I00 Giant foxtail I00 I00 I00 I O0 Cabbage .0 0 0 0Peppers 0 0 0 O Lettuce 0 0 0 0 Lima beans 0 0 0 0 Barnyard grass 0 0 204O Pigweed 0 0 0 0 Rye grass 75 25 80 Carrots 0 0 0 0 Alfalfa O O 0 OPost-emergence Evaluation at a dosage of 6 lbs/acre Test Plant SpeciesPeanuts Rice 90 Alsike clover 30 Cotton 0 Tomato 0 Wheat 0 Corn 100Meadow fescue 25 t Dallisgrass 95 Crabgrass 100 Cucumber 0 German haymillet 100 Flax I00 Lambsquartcr 100 Wild nuts 90 (liant foxtail I00Lettuce 0 Lima beans 0 Barnyard grass I00 Rye grass I00 Carrots Alfalfa0 EXAMPLE 3 This Example illustrates a typical preparation of a 5-arylmethoxy-Z-aryI-l,3-dioxane from the corresponding 5-hydroxy compoundand arylmethyl chloride. The particular product made in this Example wascis-5- (3,4-dichlorobenzyloxy)-2-phenyl-1,3-dioxane.

Sodium hydride (4.0 g, 0.101 mol) was added to cis-5-hydroxy-2-phenyl-I,3-dioxane (16.8 g, 0.1 mol) in 150 ml of xylene.The slurry was stirred at 40-50C for we hour and 3,4-dichlorobenzylchloride (19.6 g, 0.1 mol) was added. The slurry was refluxed for 6hours and then cooled and washed with 5 percent sodium bicarbonate (2 X50 ml) and water (2 X 100 ml). The solvent was stripped from the driedorganic layer under reduced pressure to give 29.8 g of solid, mp 72-78C.Two recrystallizations from benzene-ligroin gave cis-5- (3,4-dichlorobenzyloxy-Z-phenyl-l ,3-dioxane, m.p. 77-78C. VPC analysesindicated that it was nearly pure cis isomer.

EXAMPLE 4 Other herbicidally active products which may be prepared inthe same way (using the arylmethyl chloride or in certain cases thecorresponding arylmethyl bromide and the corresponding5-hydroxy-2-aryl-1,3- dioxane) include the following:

cis-5-(4-methylbenzyloxy)-2-phenyl-1,3-dioxane (m.p. 1I2.5-113C; VPCanalysis indicated nearly pure cis);

cis-5-(2-chlorobenzyloxy)-2-phenyl-1,3-dioxane (m.p. 95-96.5C; VPCanalysis indicated 85 percent cis);

cis-5-(4-chlorobenzyloxy)-2-phenyl-1,3-dioxane (m.p. l I0l I 1C; VPCanalysis indicated 87 percent cis);

cis-5-(2,4dichlorobenzyloxy)-2-phenyl-I ,3-dioxane (m.p. l l6-1 17C; VPCanalysis indicated nearly pure5-(3-methylbenzyloxy)-2-phenyl-l,3-dioxane (m.p. 6566.5C; VPC analysisindicated SI percent cis);

cis-5-(2,6-dich1orobenzyloxy)-2-phenyl-1,3-dioxane (m.p. 90-92C; VPCanalysis indicated 75 percent cis);

cis-5-(3-chlorobenzyloxy)-2-phenyl-l,3-dioxane (m.p. 57-58C; VPCanalysis indicated 87 percent cis);

cis-5-( 3 ,4-dimethylbenzyloxy)-2-phenyl-1,3-dioxane (m.p. 8890C; VPCanalysis indicated 82 percent cis);

cis-5-(2-methylbenzyloxy)-2-phenyl-l ,3-dioxane (m.p. 79-80C; VPCanalysis indicated nearly pur cis);

cis-5-(2-fluorobenzyloxy)-2-phenyl-I ,3-dioxane (m.p. -7IC; VPC analysisindicated 90 percent cis);

cis-5-(3-fluorobenzyloxy)-2-phenyl-I ,3-dioxane (m.p. 6465C; VPCanalysis indicated 79 percent cis);

cis-5-(4-fluorobenzyloxy)-2-phenyl-1,3-di0xane (m.p. 5759C; VPC analysisindicated 69 percent cis, and 2 percent trans);

cis-5-(2,5-dichlorobenzyloxy)-2-phenyl-l ,3-dioxane (m.p. 76-77C; VPCanalysis indicated nearly pure cis);

5-(2,3,6-trichlorobenzyloxy)-2-phenyl-l ,3-dioxane (here an oil productwas obtained, from which a fraction was distilled at 2l02l3C. at 10 mm;this crystallized on cooing, giving a material of m.p. 113-l14C. whichVPC analysis indicated contained 34-39 percent cis and 61-66 percenttrans);

cis-5-(2,4-dimethylbenzyloxy)-2-phenyl-1,3-dioxane (m.p. 93.5-94C; VPCanalysis indicated nearly pure cis);

cis-5-(2,5-dimethylbenzyloxy)-2-phenyl-1,3-dioxane (m.p. 102-103C; VPCanalysis indicated nearly pure cis);

cis-5-benzyl0xy-2-(2-chlorophenyl)-1,3-dioxane (m.p. 100-100.5C; VPCanalysis indicated nearly pure cis);

cis-5-benzyloxy-2-(4-chlorophenyl)-1,3-dioxane (m.p. 125-126C; VPCanalysis indicated 95 percent cis);

cis-5-benzyloxy-2-( 3-chlorophenyl)- l ,3-dioxane (m.p. 85-85.5C; VPCanalysis indicated 97 percent cis);

cis-5-( 3-trifluoromethylbenzyloxy )-2-phenyl-l ,3- dioxane (m.p. 4345C;VPC analysis indicated 84 percent cis, 9 percent trans);

cis-5-(2-cyanobenzyloxy )-2-phenyl-l ,3-dioxane (m.p. l15116C; VPCanalysis indicated nearly pure cis);

cis-5-(2-bromobenzyloxy)-2-phenyl-l ,3-dioxane (m.p. 93-94C; VPCanalysis indicated 85 percent cis, 11 percent trans);

5-(4-cyanobenzyloxy)-2-phenyl-l,3-dioxane (m.p. I- l2l 13C; VPC analysisindicated 66 percent cis, 33 percent trans);

cis-5-(Z-methoxybenzyloxy)-2phenyl-l ,3-dioxane (b.p. I190C at 10 mm;VPC analysis indicated 72 percent cis);

cis-5-benzyloxy-2-(2-bromophenyl)-l ,3 -dioxane (b.p. 2l0215C at 10' mm;VPC analysis indicated nearly pure cis);

5-benzyI0xy-2-(2-ethoxyphenyl)-1,3-dioxane (b.p. l80-l C at 10' mm; VPCanalysis indicated that it contained 11 percent cis, 27 percent trans,and 62 percent of the isomeric dioxolane);

5-benzyloxy-2-(2-methoxyphenyl)-I,3-dioxane (b.p. I-l95C at 10 mm; VPCanalysis indicated that it contained 14 percent cis, 31 percent trans,and 55 percent of the isomeric dioxolane);

5-benzyloxy-2-(2-fluorophenyl)-1,3-dioxane (b.p. I65170C at 10 mm; VPCanalysis indicated 43%, cis);

cis-5-benzyloxy-2-( 3-bromophenyl)-l ,3-dioxane (m.p. 9293C; VPCanalysis indicated nearly pure cis);

9 cis--benzyloxy--(3,5-dichlorophenyl)-1,3-dioxane (m.p. 97- 98C.; VPCanalysis indicated nearly pure cis);

cis'5-[ Z-(trifluoromethyl)benzyloxy)]-2-phenyl-l ,3- dioxane (m.p.68-69C. VPC analysis indicated nearly pure cis);

cis-5-[ 3-trifluoromethyl)benzyloxy1-2-phenyl-l ,3- dioxane (m.p.43-45C; VPC analysis indicated 84 percent cis);

cis-5-( 3-bromobenzyloxy)-2-phenyl-l ,3-dioxane;

cis-5-( 2-chlorobenzyloxy)-2-( 3-chlorophenyl)-l ,3- dioxane;

cis-5(2-fluorobenzyloxy)-2-( 3-chlorophenyl)-l ,3- dioxane;

cis-5-( Z-bromobenzyloxy)-2-(3-chlorophenyl) l ,3- dioxane;

cis-5-( 2-methylbenzyloxy)-2-( 3-chlorophenyl )-l ,3- dioxane;

cis-5-(Z-trifluoromethylbenzyloxy)-2-(3-chlorophenyl)-1 ,3-dioxane;

cis-5 -(2-chlorobenzyloxy)2-(2-fluorophenyl)-1,3- dioxane;

cis-5-(2-fluorobenzyloxy )-2-(2-fluorophenyl)-l ,3- dioxane;

cis-5-(3-fluorobenzyloxy)-2-( 2-fluorophenyl)-l ,3- dioxane;

cis-5 (4-methylbenzyloxy)-2-(2-fluorophenyl)-1,3- dioxane',

cis-5-(2-chlorobenzyloxy)-2-( 3-fluorophenyl)-l ,3- dioxane;

cis-5-( 2-fluorobenzyloxy )-2-( 3-fluorophenyl)=l ,3- dioxane;

cis-5-( 3-fluorobenzyloxy)-2-( 3-fluorophenyl )-l ,3- dioxane;

cis-5-(2-bromobenzyloxy)-2-(3-fluorophenyl)- dioxane;

cis-5-( 2-methylbenzyloxy)-2-( 3-fluorophenyl)-l ,3- dioxane;

cis-5-(4-methylbenzyloxy)-2-( 3-fluorophenyl)-l ,3- dioxane;

cis-5-benzyloxy-2-( 3-cyanophenyl )-l ,3-dioxane;

cis-5-(2-fluorobenzyloxy )-2-( 3-cyanophenyl)-l ,3- dioxane;

cis-5-(2-fluorobenzyloxy)-2-(3-bromophenyl)- 1,3- dioxane;

cis-5-benzyloxy-2-(3-methylphenyl)-l ,3-dioxane;

cis-5-(2-fluorobenzyloxy )-2-( 3-methylphenyl)- l ,3- dioxane;

cis-5-( 2-methylbenzyloxy)-2-( 3-methylphenyl)-l ,3- dioxane;

cis-5-benzyloxy-2-(3-methoxyphenyl)-l',3-dioxane;

cis-5-( 2-fluorobenzyloxy )-2-( 3-methoxyphenyl )-l ,3- dioxane;

cis-5-(2-methylbenzyloxy)-2-(3-methoxyphenyl)- 1,3-dioxane;

cis-5-( 3-fluorobenzyloxy )-2-phenyl-l ,3-dioxane.

EXAMPLE 5 This Example illustrates the preparation of intermediatesuseful in the manufacture of compounds listed in EXAMPLE 4.

(5a) 2,5-dichlorobenzyl bromide A solution of 8.0 g 2,5-dichlorotolueneand 0.5 g benzoyl peroxide in 75 ml carbon tetrachloride was heated toreflux temperature. To this was added portionwise 9.0 gN-bromosuccinimide. The resulting solution was refluxed for 5 hours. Themixture was cooled to room temperature, filtered and washed successivelywith two 50 ml volumes of 5 per cent aqueous sodium bicarbonate, two 50ml volumes of 5 per cent aqueous sodium sulfite and two 50 ml volumes ofwater. The mixture was dried over magnesium sulfate, filtered, andevaporated under reduced pressure to a yellow oil. The oil was distilledand that fraction distilling at 7578C/O.5mm (2,5-dichlorobenzyl bromide)crystallized upon cooling, m.p. 3940C.

(5b) 2,3,6-trichlorobenzyl bromide (b.p. 132134C at 4 mm) was made bythe foregoing method, substituting 2,3,6-trichlorotoluene for the 2,5-dichlorotoluene.

(5c) 5-hydroxy-2-(2-chlorophenyl)-1,3-dioxane A mixture of 140 g2-chlorobenzaldehyde, 92 g glycerol and 4 ml 40 per cent sulfuric acidwas heated under a carbon dioxide atmosphere at 100C for 6 hours. Aftercooling the reaction mixture to room temperature, the resultant oil wasdissolved in ether. The ether solution was washed with a saturatedaqueous potassium carbonate solution and then dried by magnesiumsulfate. The solution was then filtered and evaporated under reducedpressure. A small amount of HCl was bubbled through the resulting oil;which oil was then placed under refrigeration for several hours. Sincecrystallization did not occur, the oil product was dissolved in ether;the ether solution was washed with two lOO ml volumes of 1 per centammonium hydroxide and with water, dried over magnesium sulfate,filtered, and evaporated in vacuo. The resultant oil was distilled andthat fraction distilling at ll7-l l 8"C/l0"' mm contained5-hydroxy-2-(2chlorophenyl)-l ,3-dioxane.

(5d) 5-hydroxy-2-(4-chlorophenyl)-l,3-dioxane Using the method ofExample 21, 42 g 4- chlorobenzaldehyde, 27.6 g glycerol and 4 ml 40 percent sulfuric acid were reacted to form 5-hydroxy-2-(4-chlorophenyl)-l,3-dioxane. The reaction mixture was dissolved in benzeneand washed successively with two 50 ml volumes of 5 per cent aqueoussodium bicarbonate, two 50 ml volumes aqueous sodium bisulfite and twoml volumes of water. The benzene solution was dried with magnesiumsulfate, filtered and evaporated under reduced pressure to form an oilwhich crystallized, m.p. 95l0OC (recrystallized from benzeneligroin).

(5e) 2-(2-bromophenyl)-5-hydroxy-l,3-dioxane A solution of 25 g2-bromobenzaldeyde, 12.4 g glycerol and 1 ml 40 per cent sulfuric acidin 50 ml benzene was maintained with stirring at 80-l 00C for 24 hours.The resulting solution was washed with an aqueous potassium carbonatesolution, dried with magnesium sulfate and evaporated under reducedpressure. The oil product was distilled, and that fraction distilling at148l 50C/l0' mm contained 2-(2-bromophenyl)-5- hydroxy-l ,3-dioxane.

(5f) 2-(2-ethoxyphenyl)-5-hydroxy-1,3-dioxane Using the method ofExample 5e, 30 g 2- ethoxybenzaldehyde was reacted with 18.4 g glycerolto form 2-(2ethoxyphenyl)-5-hydroxy-i,3-dioxane, crude b.p. l40-l48C/E0mm.

(5g) 5-hydroxy-2-(2-methoxyphenyl)- l ,3-dioxane Using the method ofExample 5e, 40.8 g 2- methoxybenzaldehyde and 27.6 g glycerol werereacted to form 5-hydroxy-2-(Z-methoxyphenyl)-l,3- dioxane, crude b.p.150l55C lit) mm.

(5h) 2-(2-fluorophenyl)-5-hydroxy-1,3-dioxane Using the method ofExample g, except no solvent was necessary, 24.8 g 2-fluorobenzaldehydeand 18.4 g glycerol were reacted to form 2-(2-fluorophenyl)-5- hydroxy-l,3-dioxane. The product was cooled and dissolved in 100 ml ether. Theether solution was washed with an aqueous potassium carbonate solution,dried with magnesium sulfate, filtered and evaporated under reducedpressure. The resultant oil was distilled, and that fraction distillingat 140145C/10 mm contained 2-(2-fluorophenyl)-5-hydroxy-l ,3-dioxane.

(5i) 2-(3-bromophenyl)-5-hydroxy-1,3-dioxane A mixture of 27.7 g3-bromobenzaldehyde, 13.8 g glycerol and 2 ml 40 per cent sulfuric acidwas heated with stirring at 100110C for 40 hours. The mixture was thencooled, 200 ml benzene was added and the mixture was heated at 8085Cuntil the theoretical amount of water produced during the reaction wascollected. The benzene solution of potassium carbonate was diluted with200 ml ether. The benzene solution was washed with three 100 ml volumesof water, dried over magnesium sulfate and evaporated. The oil productwas distilled and that fraction which distilled at l31134C/5 X mm wasused directly for synthesis of5-benzyloxy-2-(3-bromophenyl)-1,3-dioxane.

EXAMPLE 6 This Example illustrates the production ofS-benzyloxy-l,3-dioxane and compounds in which the benzyloxy groupcarries a Y substituent.

(a) 12.0 g (0.066 mol) of 2-benzyloxy-l,3- propane-diol, 2.0 g oftrioxymethylene, 0.1 g of p-toluenesulfonic acid and 100 ml of benzenewere placed in a flask equipped with a stirrer, condenser and Dean-Stark moisture trap. The flask was heated to 80C and refluxing wascontinued until 1.4 ml H O was collected. The mixture was then cooled toroom temperature, washed twice with 100 ml portions of aqueous 2 percentsolution of sodium bicarbonate, and then twice with 100 ml portions ofwater. The washed benzene layer was then dried over magnesium sulfate;the latter drying agent was then filtered off and the solvent wasremoved by evaporation under reduced pressure. The remaining oil wasthen distilled to recover a fraction (S-benzyloxy-l,3-dioxane) whichdistilled at a pot temperature of 7280C at 10 mm.

(b) In another method of preparing the S-benzyloxy-1,3-dioxane, thestarting material was 5- hydroxy-1,3-dioxane (Tetrahedron 7, 10-18(1959)). The latter was prepared by first reacting glycerol withtrioxymethylene, in the presence of HCl as a catalyst to form a mixtureof cyclic acetals (J. Am. Chem. Soc. 50, 3124 (1928)) which was thenesterified with benzoyl chloride, in the presence of pyridine, yieldingon recrystallization the benzoate of 5-hydroxy-1,3-dioxane melting at7172C (J. Am. Chem. Soc. 50, 3120 (1928)). This ester was then split byreaction with sodium methylate in chloroform, to produce the purified5-hydroxy-l,3-dioxane which was taken off as a cut boiling at 9596C at22 mm. Three grams (0.029 mol) of the latter product and 100 ml ofbenzene were placed in a flask equipped with a stirrer, condenser,thermometer and addition funnel. While stirring, 1.1 g of sodium hydridewas added portionwise; hydrogen evolved. Next, after the resultingslurry had been kept at room temperature for 1% hour without furtheraddition of ingredients while stirring continued, 3.65 g of benzylchloride was added dropwise over a fifteen minute period. When all thebenzyl chloride had been added the mixture was heated to C andmaintained at this temperature for 24 hours while stirring continued.The slurry thus obtained was then washed twice with 100 ml portions ofwater and the resulting organic layer was dried over MgSO This dryingagent was then filtered off and the solvent was removed under reducedpressure, yielding an oil which was then distilled under reducedpressure to give a fraction (5-benzyloxy-l,3- dioxane) boiling at 80-82Cat 0.15 mm and having an estimated purity of about percent.

The foregoing methods may be used in the preparation of the followingherbicidal compounds: 5-(2- chlorobenzyloxy)-1,3-dioxane;5-(2-fluorobenzyloxy)- 1,3-dioxane; 5-(2-methylbenzyloxy)-1,3-dioxane;and 5-(4-methylbenzyloxy)-1,3-dioxane. In such preparations the2-arylmethoxy-l ,3-propane-diol used as a starting material can beprepared by the acid hydrolysis (J. Am. Chem. Soc. 74, 4466 (1952)) ofthe corresponding 5-arylmethoxy-2-phenyl-1,3-dioxane. Alternatively,5-hydroxy-1,3-dioxane can be etherified with the substituted benzylchloride or bromide, in which the substituent is as named above.

EXAMPLE 7 cis-5-(2,6-Dichlorobenzyloxy)-2-phenyl-l ,3-dioxane Sodiumhydride (2.0 g of6l percent, 0.05 mole) was added tocis-5-hydroxy-2-phenyl-l ,3-dioxane (8.4 g, 0.047 mole) in 150 ml ofxylene. The slurry was stirred at 40 for 1 hour and 2,6-dichlorobenzylbromide 12.0 g, 0.05 mole) was added. The slurry was heated at 1 10 for6 hours, then filtered to remove the precipitated solid. The filtratewas concentrated in vacuo to give 22.6 g of yellow oil which solidifiedon standing, m.p. 6584C. Recrystallization from benzenepctroleum ethergave 10.8 g of white solid, mp. '71-73C. Further purification gave awhite solid, mp. *92C. Analysis of VPC showed the product to be 75percent cis-5- (2,6-dichlorobenzyloxy)-2-phenyl-1,3-dioxane and 25percent trans-5-(2,6-dichlorobenzyloxy)-2-phenyl-l ,3- dioxane.

EXAMPLE 8 cis-5-(Z-Methylbenzyloxy)-2-phenyl-l ,3-dioxane Sodium hydride(2.0 g of 61 percent, 0.05 mole) was added tocis-5-hydroxy-2-phenyl-1,3-dioxane (8.5 g, 0.05 mole) in 150 ml ofxylene. The slurry was stirred at ambient temperature for 0.5 hour and2- methylbenzyl bromide (9.3 g, 0.05 mole) was added. The slurry washeated at C for 6 hours, cooled, and washed with water (2 X 75 ml). Theorganic layer was separated, dried over magnesium sulfate andconcentrated to give 12.4 g of product, m.p. 77'82C. Recrystallizationfrom benzene-ligroin gave 5.3 g, m.p. 78-79C. Analysis by VPC indicatedthe product to be 100 percent cis-5-(2-methylbenzyloxy)-2-phenyl-l,3-dioxane.

EXAMPLE 9 cis-5-(2-Fluorobenzyloxy )-2-phenyll ,3-dioxane Using themethod of Example 8, cis-5-hydroxy-2- phenyll,3-dioxane (8.4 g, 0.047mole) was reacted with sodium hydride (2.0 g of61 percent, 0.047 mole).The reactant sodium salt was reacted with 2- fluorobenzyl chloride (7.2g, 0.05 mole) to give, after recrystallization from benzene-ligroin, 2.8g of white solid, mp. 6567C, and on further recrystallization,

a solid, mp. 70-71C. Analysis by VPC indicated the product to be 90percent cis--(2-fluorobenzyloxy)-2- phenyl-1,3-dioxane.

EXAMPLE cis-5-(2-Bromobenzyloxy)-2-phenyl-1,3-dioxane Sodium hydride(2.0 g of6l%, 0.05 mole) was added to 5-hydroxy-2-phenyl-l,3-dioxane(8.4 g, 0.047 mole) in 150 ml of dioxane. The slurry was stirred atambient temperature for 0.05 hour and 2-bromobenzyl bromide (12.5 g,0.05 mole) was added. The slurry was heated at 100C. for 12 hours,cooled and washed with water (2 X 100 ml). The organic layer wasseparated, dried over magnesium sulfate and concentrated to give 66.2 gof solid, which on recrystallization from benzeneligroin gave 8.5 g ofsolid, mp. 909lC. Further recrystallization gave a solid, mp. 93-94C,which was shown by VPC analysis to be 85 percent cis-5-(2-bromobenzyloxy)-2-phenyl-1,3-dioxane and 11 percenttrans-5-(2-bromobenzyloxy)-2-phenyl-1 ,3- dioxane.

EXAMPLE 1 1 cis-5-[2-(Trifluoromethyl)benzyloxy1-2-phenyl-1,3- dioxaneSodium hydride (4.0 g of 61 percent, 0.01 mole) was added to5-hydroxy-2-phenyl-1,3-dioxane (18.0 g, 0.1 mole) in 150 ml of benzene.The slurry was stirred at ambient temperature for one hour and2-(trifluoromethyl)benzyl bromide (23.9 g, 0.1 mole) was added. Theslurry was heated at reflux for hours, cooled and washed with water (2 X100 ml). The organic layer was separated, dried over magnesium sulfateand concentrated to give 28.1 g of yellow oil which crystallized to givea solid, mp. 58-60C. Recrystallization of the solid from benzene-ligroingave 10.8 (m.p. 65-66C which on further recrystallization gave a solid,mp. 68-69C. Analysis by VPC indicated that product to be essentiallypure cis-5-[ 2-trifluoromethyl )benzyloxy Z-phenyl-l ,3-dioxane.

EXAMPLE 12 cis-5-Benzyloxy-2-(3-methylphenyl)-1,3-dioxane A. Preparationof 5-Hydroxy-2-(3-methylphenyl)- 1,3-dioxane A mixture of3-methylbenzaldehyde (24.0 g, 0.2 mole), glycerol (18.4 g, 0.2 mole) and40 percent sulfuric acid (2.0 ml) in 150 ml of benzene was heated undera Dean-Stark apparatus until no more water was collected (approximately2.5 hours). The mixture was cooled, neutralized with potassiumcarbonate, diluted by the addition of 200 ml of ether and the ethersolution was washed with water (3 X 100 ml). The organic layer was driedover magnesium sulfate and concentrated to give a residue of 25.1 g ofthe desired 5- hydroxy-2-(3-methylphenyl)-l,3-dioxane n 1.5346.

B. Preparation of 5-Benzyloxy-2-(3-methy1phenyl)- LIB-dioxane A slurryof sodium hydride (2.1 g 0.08 mole in 100 ml of xylene and 100 ml ofbenzene was stirred at ambient temperature while5-hydroxy-2-(3-methylphenyl)- 1,3-dioxane (15.9 g, 0.08 mole) was addeddropwise during 1 hour. Stirring was continued for 1 hour and to themixture was added benzyl chloride (10.4 g, 0.08 mole) during 0.5 hour.This mixture was heated under reflux for 22 hours, cooled, filtered andthe filtrate washed with water (2 X 250 ml). The washed solution wasdried over magnesium sulfate and concentrated under reduced pressure togive 20.9 g of oil which distilled at 2 X 10 mm. to give three fractionsdistilling respectively at 102l33C (cut 1); 133-l41C (out 2); and 141C(cut 3). Analysis of the various cuts indicated that cut 3 wasessentially pure cis-S-benzyloxy- 2-(3-methylphenyl)-l,3-dioxane, 2.1 g,m.p. 68-70C and this cut was used in further studies.

EXAMPLE 13 5 -Benzyloxy-2-( 3-fluoropheny1)- 1 ,3-dioxane A. Preparationof 5-hydroxy-2-(3-fluorophenyl)-l ,3- dioxane A mixture of3-fluorobenzaldehyde (24.8 g, 0.2 mole), glycerol (18.4 g, 0.2 mole) and40 percent sulfuric acid (2.0 ml) in benzene (200 ml) was heated withstirring under a Dean-Stark apparatus until water ceased to collect(approximately 2.5 hours). The mixture was cooled, neutralized withpotassium carbonate and, after adding 200 ml of ether, washed with water(3 X 100 ml). The washed solution was dried over magnesium sulfate andconcentrated under reduced pressure to give 29.0 g of colorless oilwhich was distilled under 0.025 mm using a short path distillationapparatus to give 18.9 g, n 1.5160, of 5-hydroxy-2-(3-fluorophenyl)-1,3-dioxane which distilled at a bath temperature of86-105C.

B. Preparation of 5-Benzyloxy-2-(3-fluorophenyl)- 1,3-dioxane A slurryof sodium hydride (3.7 g of 62 percent, 0.096 mole) in benzene (100 ml)and xylene (100 ml) was stirred at ambient temperature while5-hydroxy-2- (3-fluoropheny1)-l,3-dioxane (18.9 g, 0.096 mole) was addeddropwise, during 1 hour. This mixture was stirred one additional hour,then to it was added benzyl chloride (12.2 g, 0.096 mole) during 1%hour. The mixture was heated under reflux for 18 hours, cooled, filteredand the filtrate washed with water (2 X 200 ml). The washed solution wasdried over magnesium sulfate and concentrated to give 19.7 g of oilwhich was distilled under 2 X 10 mm pressure to give three fractionsdistilling at bath temperature of 98-119C (cut 1); 119-l39C (cut 2); and139-143C (cut 3). Cut 2 (9.1 g) was found by nmr analysis to be amixture of cis and trans-dioxanes and the corresponding dioxolane. Cut 3(1.5 g, m.p. -71C was found by nmr to be percentcis-S-benzyloxy-2-(3-fluorophenyl)-1,3- dioxane and this cut was used infurther studies.

EXAMPLE l4 5-( 2-lFluorohenzyloxy )-2-( 3-chlorophenyl )-1 ,3- dioxaneA. Preparation of 5-lrilydroxy-2-( 3-chlorophenyl)- 1,3-dioxane Amixture of 3-chlorobenzaldehyde (28.1 g, 0.2 mole), glycerol (18.4 g,0.2 mole) and p-toluenesulfonic acid (0.1 g) in ml of benzene was heatedat reflux under a Dean-Stark apparatus until water was no longercollecting (3.6 ml). The solution was cooled, washed with 2 percentsodium bicarbonate solution (2 X 100 ml) and with water (2 X 100 ml).The washed solution was dried over magnesium sulfate and concentratedunder reduced pressure. The oil remaining was distilled to give 18.1 gof colorless liquid which distilled at a pot temperature of 124-128Cunder 1 X 10* B. Preparation of cis--(2-Fluorobenzyloxy )-2-(3-chloro-phenyl)-1,3-dioxane Sodium hydride (4.0 g of 60 percent, 0.1mole) was added in small portions to a solution of S-hydroxy-2-(3-chlorophenyl)-l ,3-dioxane (21.5 g, 0.1 mole) in a mixture of 75 ml ofbenzene and 75 ml of xylene. After all sodium hydride had been added,the slurry was stirred at ambient temperature for 15 hour. To themixture was added dropwise during fifteen minutes 2-fluorobenzylchloride (14.4 g, 0.1 mole) and the mixture was heated under reflux forhours. The mixture was cooled, washed with water (2 X 100 ml), driedover magnesium sulfate and concentraed under reduced pressure. The oilwhich remained was crystallized from benzeneligroin to give 3.6 g ofsolid, m.p. 73-75C. Analysis by nmr indicated the product to beessentially pure cis-S-(2-fluorobenzyloxy)-2-(3-chlorophenyl)-1,3-dioxane. Recrystallizationgave a solid, m.p. 8586C.

EXAMPLE 5-(2-Fluorobenzyloxy )-2-( 3-fluorophenyl)-l ,3- dioxane Usingthe procedure of Example 8, 5-hydroxy-2-(3- fluorophenyl)-1,3-dioxane(16.8 g, 0.085 mole) in 150 ml of benzene was reacted with sodiumhydride (3.4 g

i of 60 percent) and the sodium salt thus formed was reuct found by nmranalysis to contain 30 percent cis-S- (2-fluorobenzyloxy)-2-(3-fluorophenyl )-l ,3-dioxane.

EXAMPLE l6 5-Benzyloxy-2-(3-benzyloxyphenyl)-1,3-dioxane A mixture of2-benzyloxy-1,3-propanediol (18.0 g, 0.1 mole), 3-benzyloxybenzaldehyde(21.2 g, 0.1 mole) and p-toluenesulfonic acid (0.1 gram) in 150 ml ofbenzene was heated at reflux under a Dean-Stark apparatus untilcollection of water ceased (1.8 ml). The solution was washed with 2percent sodium bicarbonate (2 X 100 ml) and with water (2 X 100 ml),then dried over magnesium sulfate and concentrated to give 34.2 g ofbrown oil. Recrystallization from benzeneligroin gave 22.5 g of solid,m.p. 77-78C. nmr analysis of this solid indicated it to contain 31percent cis-5- benzyloxy-2-( 3-benzyloxyphenyl)-l ,3-dioxane.

EXAMPLE 17 5-(2-Methylbenzyloxy)-2-(3-chloropheny1)-1,3- dioxane Usingthe procedure of Example 9 5-hydroxy-2-(3- chlorophenyl)-1,3-dioxane(21.5 g, 0.1 mole) was reacted with 2-methylbenzyl chloride (14.0 g, 0.1mole) to give a heavy oil, which on distillation under 1 X 10" mmpressure gave 12.5 g of product which distilled at a pot temperature of160l70C. Analysis by nmr indicated this product to contain 18 percentcis-5-(2- methylbenzyloxy)-2-(3-chlorophenyl)-1 ,3-dioxane.

EXAMPLE 18 5-(4-Methylbenzyloxy)-2-phenyl-l,3ldioxanecis-5-Hydroxy-2-phenyl-l,3-dioxane (16.8 g, 0.1 mole) was reacted with4-methylbenzyl chloride (14.0

g, 0.1 mole) using the procedure of Example 2. When the reaction mixturehad cooled, solid began to separate, thus the entire reaction mixturewas concentrated under reduced pressure. The solid product was slurriedwith water and filtered. The filter cake was dried in a vacuum oven togive 23.2 g of solid, m.p. lO6109C. Recrystallization frombenzene-ligroingave 9.1 g, m.p. 1091 10C. A second recrystallizationraised the m.p. to 1l2.5113C. Analysis by VPC indicated the product thusobtained was nearly pure cis-5-(4-methylbenzyloxy)-2-phenyl-1,3-dioxane.

EXAMPLE 19 5-Benzyloxy-2-(3-chlorophenyl)-1,3-dioxane A slurry of5-hydroxy-2-(3-chlorophenyl)-1,3- dioxane (21.5 g, 0.1 mole) in 200 mlof xylene was stirred at ambient temperature while sodium hydride (4.0 gof 61 percent) was added in small portions. When all the hydride hadbeen added, the slurry was stirred for an additional half hour. Benzylchloride (14.2 g, 0.1 mole) was added dropwise during fifteen minutes tothe stirred mixture and the slurry was then heated at 100C for tenhours. The mixture was cooled to room temperature, washed with water (2X 100 ml), dried over magnesium sulfate and concentrated. The oil whichremained (20.2 g) was recrystallized from benzene-ligroin to give 4.8 gof solid, m.p. 83-84C. Recrystallization gave a solid, m.p. 85-85.5C.Analysis by VPC indicated this product to be 97 percent cis-5-benzyloxy-2-( 3-chlorophenyl l ,3-dioxane.

EXAMPLE 20 5-Benzyloxy-2-(2-fluorophenyl l ,3-dioxane A. Preparation of2-(2-Fluorophenyl)-5-hydroxy- 1,3-dioxane A mixture of2-fluorobenzaldehyde (24.8 g, 0.2 mole), glycerol (18.4 g, 0.2 mole) and40 percent sulfuric acid (2 ml) was heated at 80-100C for 12 hours. Themixture cooled to room temperature and 100 ml of ether was added. Thesolution was washed with 2 percent potassium carbonate solution, driedover magnesium sulfate and concentrated under reduced pressure. The oilwhich remained (28.7 g) was distilled under 1 X 10' mm to give a product18 g) which distilled at a pot temperature of 145C. This product wasidentified by infrared and elemental analysis as 5-hydroxy-2-(2-fluorophenyl)-1,3-dioxane.

B. Preparation of 5-Benzyloxy-2-(2-fluorophenyl)- 1,3-dioxane5-Hydroxy-2-(2-fluorophenyl)-1,3-dioxane (18.0 g, 0.09 mole) was reactedwith sodium hydride and benzyl chloride (13.0 g, 0.09 mole) as describedin Example 2, except that the slurry was heated at 80100C for 12 hours.The product was isolated in the manner described in Example 2 to give12.1 g of oil which was distilled under 1 X 10 mm to give a product (6.2g) which distilled at a pot temperature of 170C. VPC analysis of thisproduct indicated it to contain 32 percentcis-5-benzyloxy-2-(2-fluorophenyl )-l ,3- dioxane.

EXAMPLE 21 5-Benzyloxy-2-( 3-methoxyphenyl l ,3-dioxane Using the methodof Example 16, 2-benzyloxy-l ,3- propane-diol (18.0 g, 0.1 mole), and 3

2. Method as in claim 1, in which Rr is a phenyl radical having at leastone non-hydrogen substituent in an ortho position.
 3. Method as in claim1 in which R2 is a phenyl radical having at least one non-hydrogensubstituent in a meta position.
 4. Method as in claim 1 in which R2a ishydrogen.
 5. Method as in claim 1 in which R2 is aromatic and has afluoro substituent.
 6. Method as in claim 2 in which said phenyl radicalhas a fluoro substituent in an ortho position.
 7. Method as in claim 2in which said phenyl radical has a chloro substituent in an orthoposition.
 8. Method as in claim 2 in which said phenyl radical has amethyl substituent in an ortho position.
 9. The method as in claim 1 inwhich the compound is cis-5-benzyloxy-2-phenyl-1,3-dioxane;cis-5-(2-fluorobenzyloxy)-2-phenyl-1,3-dioxane;cis-5-(2-methylbenzyloxy)-2-phenyl-1,3-dioxane;cis-5-benzyloxy-2-(3-chlorophenyl)-1,3-dioxane; 5-benzyloxy-1,3-dioxane;cis-5-benzyloxy-2-(2-fluorophenyl)-1,3-dioxane;cis-5-(4-methylbenzyloxy)-2-phenyl-1,3-dioxane;cis-5-(2-bromobenzyloxy)-2-phenyl-1,3-dioxane;cis-5-(4-fluorobenzyloxy)-2-phenyl-1,3-dioxane;cis-5-(3-fluorobenzyloxy)-2-phenyl-1,3-dioxane;cis-5-(2,6-dichlorobenzyloxy)-2-phenyl-1,3-dioxane;cis-5-(2-chlorobenzyloxy)-2-phenyl-1,3-dioxane;cis-5-benzyloxy-2-(3-fluorophenyl)-1,3-dioxane;cis-5-(2-fluorobenzyloxy)-2-(3-fluorophenyl)-1,3-dioxane;cis-5-(2-fluorobenzyloxy)-2-(3-methylphenyl)-1,3-dioxane;cis-5-(2-fluorobenzyloxy)-2-(3-chlorophenyl)-1,3-dioxane;cis-5-benzyloxy-2-(3-benzyloxyphenyl)-1,3-dioxane;cis-5-benzyloxy-2-(3-methoxyphenyl)-1,3-dioxane;cis-2-(3-chlorophenyl)-5-(2-methylbenzyloxy)-1,3-dioxane;r-2-chloromethyl-c-5-(2-fluorobenzyloxy)-5-methyl-1,3-dioxane;r-2-ethyl-c-5-(2-fluorobenzyloxy)-5-methyl-1,3-dioxane;r-2-ethyl-c-5-(2-methylbenzyloxy)-5-methyl-1,3-dioxane;r-2-ethyl-5-methyl-c-5-(2-methylbenzyloxy)-1,3-dioxane; orcis-5-(2-fluorobenzyloxy)-2-(2-furyl)-1,3-dioxane.
 10. Method of claim 1in which R2a is hydrogen and in which each of the substituents R2, R5and Rr has a molecular weight below 125 when it is aliphatic and amolecular weight below 190 when it contains a ring.
 11. Method as inclaim 1 in which the compound is applied as a preemergence treatment tothe soil of a soybean field.
 12. Method as in claim 1 in which thecompound is applied as a preemergence treatment to the soil of a cottonfield.